1. Field of the Invention
The present invention relates generally to a vehicular height regulation system for regulating the vehicular height within a predetermined target height range. More specifically, the invention relates to a vehicular height regulation system which is variable of sensitivity level in detecting vehicular height change out of the target height range.
2. Description of the Background Art
One of typical vehicular height control system has been disclosed in the Japanese Patent First (unexamined) Publication (Tokkai) Showa 58-112817. In the disclosed, the system monitors vehicular height level and compares the monitored height level with a predetermined upper and lower limit defining a target height range set about a predetermined target height. When the vehicular height monitored is lower than the lower limit, height adjustment for rising the vehicular height is performed so as to regulate the vehicular height within the target height range. On the other hand, when the vehicular height is higher than the upper limit, height adjustment is performed for lowering the height to the upper limit.
In such vehicular height regulation system has fixed height range to define the deadband about the target height level regardless of the vehicular driving condition. Therefore, sensitivity level of vehicular height variation for detecting vehicular height varying out of or into the target height range is constant at all vehicular driving condition. In such conventional vehicular height regulation system, a difficulty is encountered in determining the height range to be set about the target height level. Namely, when the height range is set at excessively narrow, then the vehicular height control system becomes excessively sensitive to the height variation so as to carry out height regulating operation to maintain the vehicular attitude even during concerning. This causes difficulty for the driver to realize the critical speed for passing the corner. Furthermore, when height adjustment is performed during cornering, vehicular steering characteristics tends to be changed toward over-steer characteristics to degrade cornering stability and drivability. On the other hand, when the height range to be set about the target height level is excessively broad, the control system may allow substantial vehicular height variation and thus allows substantial vehicular attitude changes to cause degradation of the riding comfort.